As the Republic of Ireland squad prepare for tomorrow's crucial European Championship qualifier in Portugal, the odds are that Paul McGrath will be fast asleep or guzzling from a bottle.

The Paul McGrath in question is, it must be said, barely three months old. His father, the Paul McGrath, will be present and correct in Lisbon's Stadium of Light for a game which is set to decide whether the Irish reach next summer's finals, as well as Jack Charlton's future as manager.

What is more, the Aston Villa centre-back - arguably the finest defender of his generation - will be playing his 79th international match, making him the most capped footballer in the Republic's history. Not bad for someone whose knees are perpetually reputed to be on their last legs, and whose periodic excesses have seen him cast as a sporting equivalent of Brendan Behan or Shane MacGowan.

To meet McGrath is to challenge your preconceptions. Not least about the notorious knees, which he insists are "grand". He does not pretend to be a candidate for the Temperance XI, yet it is hard to imagine anyone less like the self-destructive problem child Alex Ferguson felt compelled to sell for peanuts.

McGrath, who will be 36 next month, always exudes a massive presence and confidence on the pitch. Off it, he is almost painfully self-effacing and gently genial. Once he relaxes, without a drink in sight, he is also humorous and disarmingly frank.

For instance he is prepared to say, without a trace of conceit, that he ought to have won even more caps. "There were a lot of rough edges when I first went to Manchester United [from St Patrick's Athletic in 1982]. But I was established in the team well before I got the call. I think I should've been pushed forward earlier."

In the event it was 1985, with St Jack's era still a year away and Eoin Hand at the helm, before he received his chance as substitute for Mark Lawrenson against Italy in front of what seemed like "a million people" at Dalymount Park. The world champions won 2-1, but the newcomer started against England at Wembley a month later.

Hand was already using players - the Ealing-born, Dublin-bred McGrath among them - who qualified by virtue of a parent's birthplace. Charlton took the process to its logical conclusion. "Jack went looking for players," McGrath admits, "though none of the lads with us now just wanted a country to play for. They're Irish through and through."

He recalls that Charlton's first training session, conducted in a cramped hall, "raised a few eyebrows". Likewise his decision to make McGrath captain. "I looked around me and Liam Brady and Frank Stapleton were there, Kevin Moran too. I was in shock because I'm the quietest of lads. I'm not a shouter on the pitch.

"Now Liam is the best player I've played with for Ireland, by far. So I went to him and the others and begged them to co-operate! I told them I didn't really want to do it, but Jack said, `Just take the ball out' and I did it for five games."

By the time they went to West Germany for the European Champion- ship finals of 1988, the Republic had developed a system which maximised their relatively slender resources. McGrath's role was as midfield anchor. The group stage pitted them against England, whose Old Trafford contingent ribbed him mercilessly about the drubbing to come.

All the sweeter, then, when Ray Houghton put the Irish ahead early on. Soon afterwards, McGrath jarred his knee while "foolishly trying a shot". By half-time it had stiffened up completely.

"I was in a bad way and shouldn't have gone out. I've got the game on video and in the second half I was just chasing shadows. The lads were carrying me, which is why England came into it so strongly and probably should've won."

The Republic held on, and the party at the team's Stuttgart hotel went on until the small hours. Players supped freely with fans; something few other international sides, if any, would countenance. "We had to get them in," McGrath explains. "None of us knew how to play the fiddle."

The 1990 World Cup in Italy saw the Irish master the art of winning through without winning matches. McGrath, now under Graham Taylor's wing at Villa and still operating in midfield, had an outstanding tournament. Characteristically, he cites an incident in which he was an onlooker as the one he treasures.

"We had to win a shoot-out with Romania in Genoa to reach the quarter- finals. David O'Leary, who'd come on as sub, was running round organising everyone for the penalties. I didn't take one - I was hiding because I didn't have the bottle. Needless to say, Dave scored the winner."

A more sinister kind of bottle was to blame when McGrath twice went AWOL between Italia '90 and USA '94. It was a measure of his enduring excellence that Charlton, describing him as "a special case... the best player in Britain", kept faith with him.

"I've been foolish, but it's all part of growing up. I've done mine in public, which is the hard part, but I think I've learned from my mistakes. Jack accepted me back, and I hope I've repaid him on the pitch."

Installments are made with a consistency that belies his age and image. After the Irish stunned Italy in New York, Charlton called him "immense". But nothing, McGrath maintains, could have prepared them for the sauna heat encountered at Orlando against Mexico. "It was a ridiculous day to play football. The Mexicans ran round doing one-twos, laughing at us while we were melting.

"We thought we could bounce back, but we never got over it. We just didn't perform against Holland. We felt we'd let people down, which was a bad way to go."

Epic as the clashes with England and Italy were, the match that stands out for McGrath among the 78 to date was fought out in less glamorous surroundings. Needing to avoid defeat by Northern Ireland in Belfast to book their passage to America, the Republic hit back to draw 1-1.

"It's one I'd never want to play again because of the tension of the night. But the feeling when we got back to Dublin was fantastic. The whole city seemed to be out celebrating."

With one possible exception. To Eamon Dunphy, the tabloids' "jolly green giant" was only a "small-town hero" whose teams were actually under-achieving. Stapleton and Mick McCarthy used to leave the room when he entered. McGrath, revealing an independent streak, balances fierce loyalty to Charlton with the view that Dunphy is "good for Irish football".

"It's no use everybody patting you on the back all the time, yes-men telling you you're great. The odd comment upsets you, but that spurs you on to prove them wrong."

On the subject of motivation, Charlton warned after last month's narrow win over Latvia that he would resign if they failed to make it to England. "None of the lads want to see Jack go after all he's done for us," McGrath says. "And a few of us might be on our way if we go out, so there's every incentive."

This is not a veiled threat, rather an acceptance of the possibility that a new manager would dispense with the old guard. Nevertheless, McGrath loves representing his country and feels he is playing as well as ever. "I've no plans to retire yet. I'll be a long time not playing football, so whoever's in charge I want to go on as long as possible."

Taking the caps record off Packie Bonner would not, he concedes, be much consolation if results went against them. But the Irish, for whom victory would guarantee qualification, can still beat anyone on their day, according to McGrath. They certainly got the better of Portugal at Lansdowne Road.

After that 1-0 success, a member of the visiting entourage sought out the Republic's No 5 to ask for his shirt. Honoured though the wearer was to oblige the great Eusebio, he is unlikely to relinquish it so readily in Lisbon. It will, after all, be something to show the other Paul McGrath when dribbling begins to take on a new meaning.